Reducing reflection squint in a wireless communications network

Abstract

A method performed by a network node for configuring the reflection state of phase-shifting elements arranged to reflect radio signals between the network node and wireless devices served by the network node in a wireless communications network is provided. The method comprise obtaining radio link and / or user characteristics for different sub-bands of the operating bandwidth of the radio signals. Also, the method comprise configuring the reflection state of the phase-shifting elements by assigning different weights to the different sub-bands, wherein the weights are determined based on their respective sub-band's radio link and / or user characteristics. A network node is also provided, as well as, computer programs and carriers.

Description

[0001] REDUCING REFLECTION SQUINT IN A WIRELESS COMMUNICATIONS NETWORK TECHNICAL FIELD Embodiments herein relate to reducing reflection squint in a wireless communications network. In particular, embodiments herein relate to a network node and method therein for configuring the reflection state of phase-shifting elements arranged to reflect radio signals between a network node and wireless devices served by the network node in a wireless communications network. Further, the embodiments herein also relate to a computer program and a carrier. BACKGROUND In today’s wireless communications networks a number of different technologies are used, such as, 6G / New Radio (NR), Long Term Evolution (LTE), LTE-Advanced, Wideband Code Division Multiple Access (WCDMA), Global System for Mobile communications / Enhanced Data rate for GSM Evolution (GSM / EDGE), Worldwide Interoperability for Microwave Access (WiMax), or Ultra Mobile Broadband (UMB), just to mention a few possible technologies for wireless communication. A wireless communications network comprises network nodes, e.g. Radio Base Stations, RBSs, providing radio coverage over at least one respective geographical area forming a cell. This is commonly referred to as a Radio Access Network, RAN. The RAN is in turn connected to the core network in the wireless communications network via a so-called backhaul network. Wireless devices, also referred to as User Equipments or UEs, mobile stations, and / or wireless terminals, are served in the cells by the respective radio base station and are communicating with respective radio base station in the RAN over an air / radio interface. Commonly, the wireless devices transmit data over the air / radio interface to the radio base stations in uplink, UL, transmissions and the radio base stations transmit data over the air / radio interface to the wireless devices in downlink, DL, transmissions. In recent developments, so-called Reconfigurable Intelligent Surfaces, RISs, or similar, has emerged as a promising RAN technology. Reconfigurable Intelligent Surfaces, RISs, are tuneable reflective surfaces that may be constructed from metamaterials and comprises a number of phase-shifting elements that controls part of the propagation channel between a transmitter and a receiver, e.g. between a network node and wireless devices. The phase-shifting elements may also be referred to, for example, as reflection / reflective elements or antennas (e.g. micro-strip patches or patch antennas). The phase-shifting elements of the reflective surface have the potential to reflect the incoming signal towards a target direction by applying a different phase shift at each phase-shifting element, i.e. each phase-shifting element having a different or individual reflection state. By adjusting phase shift values, a beam gain of up to ^^^^2may be obtained at the surface, where ^^^^ is the total number of phase-shifting elements. This beam gain may be further increased by amplifying the incoming signal at the reflective surface. However, due to their low energy requirements and lower hardware costs, passive reflective structures or surfaces without any amplifiers are commonly accepted in the prior art and prototyped by many wireless technology manufacturers. Fig.1 illustrates a typical scenario or use case for a reflective surface 130, e.g. a RIS. In the example shown in Fig.1, a direct line-of-sight signal 141 between the network node 110 and the wireless device(s) 121 in the wireless communications network 100 may be blocked, e.g. due to a physical object being located between them. In this case, a reflective surface 130 may be useful to reflect the incoming signal 142 from the network node 110 towards the wireless device(s) 121, i.e. the reflected signal 144, to enable favourable radio access link conditions between the network node 110 and the wireless device(s) 121. This scenario or use case for the reflective surface 130 may commonly be referred to as blind-spot coverage. In Fig.1, the reflective surface 130 is composed by several phase-shifting elements, such as, the phase shifting element 131. To apply or tune the different phase-shifts at each phase-shifting element 131, each phase-shifting element 131 may be coupled to a phase-shifting circuit, or phase shifter, whose state may be controlled by a central controller circuit, e.g. a control unit 132. In some cases, the reflective surface 130 may be network-controlled, e.g. via a wireless control link 143. One of the main advantages of reflective surface 130 is that it does not perform any baseband operation to apply the phase shifts to the incoming signal 142 and hence the energy consumption is potentially very low. For the phase-shifting circuits applying the phase-shifts at each phase-shifting element 131, different analogue hardware units or equipments may be used, such as, e.g. pin diodes, varactor diodes, liquid crystals, etc. In this case, the reflective surface 130 becomes an analogue beamformer, which to a certain extent limits its beamforming capability. To obtain the maximum gain from the reflective surface 130, the reflective surface 130 is suitably deployed in a wireless communications network 100 such that network node-to-RIS link and the RIS-to-wireless-device link are line-of-sight paths. Furthermore, in case of defining the elevation and azimuth Angle-of-Arrival, AoA, from the network node 110 to the reflective surface 130 as (^^^^^^^^^^^^,^^^^^^^^^^^^) and the elevation and azimuth Angle-of-Departure, AoD, from surface 130 to the wireless device(s) 121 as (^^^^^^^^^^^^^^^^,^^^^^^^^^^^^^^^^), where ^^^^^^^^^^^^,^^^^^^^^^^^^^^^^are elevation angles and ^^^^^^^^^^^^,^^^^^^^^^^^^^^^^are azimuth angles, the gain of the reflective surface 130 may be determined according to Eq.1: ^^^^ = |(^^^^ ⊙ )^^^^ |2^^^^^^^^^^^^ ^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^ , (Eq. 1)where ^^^^^^^^^^^^ = ^^^^(^^^^^^^^^^^^,^^^^^^^^^^^^) is the array steering vector for the incoming wave or radio signal142, ^^^^^^^^^^^^^^^^ = ^^^^(^^^^^^^^^^^^^^^^,^^^^^^^^^^^^^^^^) is the array steering vector for the reflected wave or radio signal144, and ^^^^^^^^^^^^^^^^is the phase-shift vector of the reflective surface 130. Here, it should also be noted that the symbol ⊙ is used to denote the Hadamard product, i.e. element-wise multiplication. The array steering vector ^^^^(^^^^,^^^^) may be mathematically expressed according to Eq.2: where (^^^^^^^^ ,^^^^^^^^ , ^^^^^^^^) is the 3D coordinates of the ^^^^-th phase-shifting element, and ^^^^ is thewavelength. Here, the coordinate system may be defined such that the reflective surface130 is on the y-z plane, i.e. ^^^^^^^^ = 0, ∀^^^^ and the boresight of the reflective is at (^^^^,^^^^) =(0°, 0°).For a given ^^^^^^^^^^^^and ^^^^^^^^^^^^^^^^, the gain ^^^^ of the reflective surface 130 may be at most ^^^^2and the equality holds when the condition in Eq.3 is upheld: where ∠ is the angle operator, and[^^^^]^^^^denotes the ^^^^-th element of the vector ^^^^. Intuitively, this means that the reflective surface 130 reflects the signal with an angle shiftof −∠[^^^^^^^^^^^^]^^^^ − ∠[^^^^^^^^^^^^^^^^]^^^^ compared to the AoA, which implies that the AoD from the reflectivesurface 130 is aligned with that of the receiver, i.e. the wireless device(s) 121. Fig.2 illustrates an example of a gain of a reflective surface as a function of theazimuth AoD. In Fig. 2, a beam-pattern of a 32 x 32 reflective surface (^^^^ = 1024) withhalf-wavelength element spacing for (^^^^^^^^^^^^,^^^^^^^^^^^^) = (0°, 10°) and (^^^^^^^^^^^^^^^^,^^^^^^^^^^^^^^^^) = (0°,−60°) at27 GHz is shown. Here, it is assumed that the azimuth AoA is fixed at 10°, and that the phase shift vector ^^^^^^^^^^^^^^^^is fixed and optimized according to Eq.3 for an azimuth AoD of −60°. Hence, it may be seen in Fig.2 that the gain of the reflective surface has a peak when the azimuth AoD equals −60°, which is the target AoD. At the peak, we have a gain10 log10(^^^^2) = 10 log10((32 × 32)2) ≈ 60.2 dB. However, it should be noted that this gainis provided for frequencies about 27 GHz for which the phase shift vector is designed, which limits the effectiveness of the reflective surface across a broader bandwidth of the radio signals within a wireless communications network. SUMMARY It is an object of the present disclosure to mitigate, alleviate or eliminate one or more of the deficiencies and disadvantages of reflective surfaces in the prior art and increase the effectiveness of reflective surfaces in wireless communications networks. According to a first aspect of embodiments herein, the object is achieved by a method performed by a network node for configuring the reflection state of phase-shifting elements arranged to reflect radio signals between the network node and wireless devices served by the network node in a wireless communications network. The method comprise obtaining radio link and / or user characteristics for different sub-bands of the operating bandwidth of the radio signals. The method also comprises configuring the reflection state of the phase-shifting elements by assigning different weights to the different sub-bands, wherein the weights are determined based on their respective sub-band’s radio link and / or user characteristics. According to a second aspect of embodiments herein, the object is achieved by a network node for configuring the reflection state of phase-shifting elements arranged to reflect radio signals between the network node and wireless devices served by the network node in a wireless communications network. The network node is configured to obtain radio link and / or user characteristics for different sub-bands of the operating bandwidth of the radio signals. The network node is further configured to configure the reflection state of the phase-shifting elements by assigning different weights to the different sub-bands, wherein the weights are determined based on their respective sub- band’s radio link and / or user characteristics. According to a third aspect of the embodiments herein, a computer program is also provided configured to perform the method described above. Further, according to a fourth aspect of the embodiments herein, carriers are also provided configured to carry the computer program configured for performing the method described above. By obtaining radio link and / or user characteristics for different sub-bands of the operating bandwidth of the radio signals, the network node is able to determine and assign different weights to different sub-bands based on the respective radio link and / or user characteristics within each sub-band. For example, to weight the currently most important sub-band(s) of the radio signals more heavily than other currently less important sub-band(s) of the radio signals. Hence, the network node is further able to adapt the reflection state of the phase-shifting elements (or, in other words, adjust the phase-shifts to the reflected radio signal caused by the phase-shifting elements) according to the weighted sub-band(s) of the radio signals. This enables the network node to make a suitable selection of the frequency at which the reflection state of the phase-shifting elements is to be tuned in order to obtain the largest or maximum gain from the phase- shifting elements for the reflected radio signals across the entire bandwidth of the radio signals. It should be noted that, depending on which sub-band(s) is most heavily weighted, this will likely not be the conventionally used middle or center frequency of the operating bandwidth. This will effectively reduce or mitigate the squint or beam squint effect at more important sub-bands in the operation bandwidth of the radio signal, which will increase the effectiveness of reflective surfaces in wireless communications networks. BRIEF DESCRIPTION OF THE DRAWINGS Features and advantages of the embodiments will become readily apparent to those skilled in the art by the following detailed description of exemplary embodiments thereof with reference to the accompanying drawings, wherein: Fig.1 is a schematic illustration of a typical scenario or use case for a reflective surface in a wireless communications network, Fig.2 is a schematic illustration of a gain of a reflective surface as a function of the azimuth AoD of its reflected signal, Fig.3 is a diagram illustrating the effect of beam squint for a reflective surface, Fig.4 is a flowchart depicting embodiments of a method, Fig.5 is another schematic illustration of a typical scenario or use case for a reflective surface in a wireless communications network, Fig.6 is a diagram illustrating the gain of phase-shifting elements in a wireless communications network according to some embodiments, Figs.7-10 illustrates weighted gain distributions of phase-shifting elements in a wireless communications network according to some embodiments, Fig.11 is a block diagram depicting embodiments of a network node. DETAILED DESCRIPTION The figures are schematic and simplified for clarity, and they merely show details which are essential to the understanding of the embodiments presented herein, while other details have been left out. Throughout, the same reference numerals are used for identical or corresponding parts or steps. As part of the developing of the embodiments described herein, it has been realized that conventional Reconfigurable Intelligent Surfaces, RISs, designs are implemented using analogue RF components, which only provide a wideband reflection setting and notably thus do not include any filter distinguishing signals in the frequency domain. When using these reflective structures or surfaces and having a large operating bandwidth in a wireless communications network, there will be a so-called squint or beam squint effect. This means that the gain of a reflective surface will decrease for frequencies further away from the center frequency for which the phase-shift values of the phase- shifting elements are tuned. An example of the effect of beam squint for a reflective surface is illustrated in Fig.3. Fig.3 shows a diagram illustrating the gain of a reflective surface 130 as afunction of frequency. In this example, the reflective surface 130 has ^^^^ = 1024 phase-shifting elements and the operating bandwidth is 3 GHz, i.e. between 25.5-28.5 GHz. The reflective surface 130 reflects the incoming radio signals, e.g. the incoming radio signal 142 in Fig.1, coming from azimuth AoA of 10° towards the azimuth AoD of −60° , e.g. the reflected radio signal 144 in Fig.1. Here, the wideband phase-shifts, or phase-shifting values, for the phase-shifting elements of the reflective surface 130 are tuned and designed for the center frequency of the operating bandwidth, i.e. at 27 GHz. As seen inthe diagram, peak gain of the reflective surface 130 is equal to 20 log10 ^^^^ =20 log101024 ≈ 60.2 dB, which is obtained at the center of the operating bandwidth. Asthe frequency gets further away from the center frequency, the gain of the reflective surface gets lower. This is due to squint or beam-squint effect. At the edge frequencies of the operating bandwidth, i.e. at 25.5 and 28.5 GHz, this results in roughly 6 dB less gain for the reflective surface 130. Considering the significant loss in gains of the reflective surface 130 due to squint, a solution is required to mitigate this effect and thereby increase the effectiveness of reflective surfaces in wireless communications networks. This issue is addressed by the embodiments described herein, and is particularly advantageous over conventional phase-shift configuration techniques when the weights of the sub-bands in the operation bandwidth are not symmetric around the middle or center frequency. Of course, if all sub-bands in the operating bandwidth are assigned the same weight inferring that all sub-bands in the operating bandwidth are of the same importance, then the resulting frequency at which the reflection states of the phase- shifting elements are to be optimized will be the middle or center frequency of the operating bandwidth. On the other hand, such symmetric weightings will most likely be very rare in any practical setup. This is because it is very likely that at least one of the radio link or user characteristics for the served wireless devices, which ultimately influence the sub-band weight computation, is not symmetric across the middle or center frequency. For example, even in the unlikely event that the scheduling policy gives symmetric priorities for the wireless devices across the middle or center frequency, it is highly unlikely that the channel gains associated with such wireless devices also will be symmetric, etc. If multiple carriers, i.e. sub-bands, are used to serve one wireless device, i.e. carrier aggregation, then one carrier / sub-band will be assigned as the wireless device’s primary cell, PCell, i.e. the carrier / sub-band where the wireless device listens to broadcast and control channels. Thus, since this carrier / sub-band, or PCell, will carry most of the important control channels, it is also likely that this carrier / sub-band, or PCell, should have comparatively higher weight that the other carriers / sub-bands in order to guarantee good control channel coverage. It should also be noted that another advantage of designing the reflection states of the phase-shifting element 131 at the network node 110 according to the embodiments described herein is that the energy consumption and / or complexity at the phase-shifting elements 131 is not increased, which may result in simpler designs of Reconfigurable Intelligent Surfaces, RISs. Examples of embodiments of a method performed by a network node 110 for configuring the reflection state of phase-shifting elements 131 arranged to reflect radio signals between the network node 110 and wireless devices 121 served by the network node 110 in a wireless communications network 100, will now be described with reference to the flowchart depicted in Fig.4. Fig.4 is an illustrated example of actions or operations which may be taken by the network node 110 in a wireless communications network 100 as shown in Fig.1. According to some embodiments, the phase-shifting elements 131 form part of a Reconfigurable Intelligent Surface, RIS, arrangement 130, i.e. a reflective surface. The method may comprise the following actions. Action 401 The network node 110 obtains radio link and / or user characteristics for different sub-bands of the operating bandwidth of the radio signals. This means, for example, that the network node 110 may use information that is conventionally readily available to the network node 110, or conventionally be determined by the network node 110 in the wireless communications network 100, in order to get specific information applicable for each of the different sub-bands. According to some embodiments, the radio link characteristics for the different sub-bands of the operating bandwidth of the radio signals may comprise one or more of: a bandwidth assigned to the sub-band; a primary cell, pCell, bandwidth assigned to the sub- band; an AoA of radio signals to the served wireless devices 121 in the sub-band; an AoD of radio signals to the served wireless devices 121 in the sub-band; a type of a radio link in the sub-band; a quality or gain of a radio link to a served wireless device(s) 121 in the sub-band; a path-loss of a radio link to a served wireless device(s) 121 in the sub-band; and a Signal-to-Noise Ratio, SNR, of a radio link to a served wireless device(s) 121 in the sub-band. This means, for example, that network node 110 may obtain characteristics or qualities related to the radio link that may subsequently used for determining the weights for each sub-band below in Action 402. Here, it should be noted that examples of types of radio links in the sub-band may, for example, radio links used for control or data transmissions. According to some embodiments, the user characteristics for the different sub- bands of the operating bandwidth of the radio signals may comprise one or more of: the number of served wireless devices 121 in the sub-band; a Quality-of-Service, QoS, requirement of one or more served wireless devices 121 in the sub-band; a priority of one or more served wireless devices 121 in the sub-band; and a priority of a control or data channel to / from one or more served wireless device(s) 121 in the sub-band. This means, for example, that network node 110 may obtain user characteristics or priorities related to the wireless devices 121 being served by the radio link that may subsequently used for determining the weights of each sub-band below in Action 402. Action 402 After obtaining the radio link and / or user characteristics for the different sub-bands in Action 401, the network node 110 configures the reflection state of the phase-shifting elements 131 by assigning different weights to the different sub-bands, wherein the weights are determined based on their respective sub-band’s radio link and / or user characteristics. This means, for example, that the network node 110 may use the obtained radio link characteristics (e.g. radio link gains or SNRs, the type of link (control or data) at a specific frequency, etc.) and / or obtained user characteristics (e.g. user priorities, etc.) to determine weights for each sub-band in the operating bandwidth. Hence, based on which criterion is deemed to be the most important for the radio signals and radio link at the moment, the network node 110 is thus able to obtain the necessary information, e.g. any of the obtained radio link or user characteristics described above in Action 401, onto which the weights for the different sub-bands are to be determined, and then subsequently assign the determined weights to the different sub-bands. This may thus serve as a basis for the configuring the reflection states of the phase-shifting elements 131. Here, it should be noted that the term “reflection state of the phase-shifting elements” may refer to the actual individual phase-shifts, or phase-shifting values or settings, of each phase-shifting element, but may also refer to the overall phase-shifting property, e.g. reflection direction, of a reflective surface comprising any number of phase-shifting elements, such as, for example, a reflective surface comprising a metasurface tuneable by, e.g. switches, PIN-diodes, etc., to achieve a certain overall phase-shifting property of the reflective surface. In some embodiments, the weight ^^^^^^^^ associated with a sub-band ^^^^, may bedetermined according to Eq.4: ^^^^^^^^ = ∑^^^^^^^^^^^^=1 ^^^^^^^^ ^^^^^^^^^^^^(Eq.4) where ^^^^^^^^^^^^is the current weight given to a radio link or user characteristic, ^^^^^^^^is a pre-defined weight for a radio link or user characteristic ^^^^, and ^^^^^^^^is the number of users at sub-band ^^^^. Here, current non-negative real valued radio link or user characteristic weights {^^^^^^^^^^^^} may be assigned to different sub-bands based on any of the obtained radio link or user characteristics described above in Action 401. For example, in case a wireless device(s) 121 has a strong line-of-sight radio link towards the network node 110 and therefore does not require the phase-shifting elements 131 to communicate reliably, i.e. the radio link characteristics or qualities for the wireless device(s) 121 in a sub-band are good, a comparably lower weight may be given to such a radio link characteristic or quality for that sub-band. Similarly, in case a wireless device(s) 121 with a high priority is scheduled in a sub-band, a comparably larger weight may be given to such a user characteristic or quality for that sub-band. According to another example, since data may be decoded by the wireless device(s) 121 only if the related control channel information is correctly decoded by the wireless device(s) 121, control channels may be prioritized over data channels and a comparably higher weight may be given to such a radio link characteristic or quality of that sub-band, i.e. comparably larger weights may be assigned to the corresponding sub- bands carrying control information that the corresponding sub-bands carrying data information. In other words, the type of radio link that is carrying control information, i.e. comprise a control channel(s), may be prioritized over the type of radio links that is carrying data information, i.e. comprise a data channel(s). Optionally, according to some embodiments, the radio link or user characteristic weights assigned to different sub-bands may also be binary, i.e. zeros (0) or ones (1). In this case, it should be noted that such binary weights may allow for simpler mappings between the radio link or user characteristics and the weights assigned to the different sub-bands, as compared to, for example, the embodiments using non-negative continuous real valued weights as described above. Here, for example, if a radio link or user characteristic condition is met, the radio link or user characteristic weight may be set to one (1). Otherwise, it may be set to zero (0). More specifically, if the radio link or user requirements of wireless device(s) 121 may be met without the assistance of the phase-shifting elements 131, i.e. the wireless device(s) 121 is able to communicate reliably with the network node 110 on its own, a radio link or user characteristic weight equal to zero (0) may be given to such a radio link characteristic or quality for that sub-band. This means that the radio link or user characteristic of these wireless device(s) 121 are not relevant for the determination and configuration of the reflection state of the phase-shifting elements 131. This is because, in this case, the wireless device(s) 121 may have good cell coverage or even a clear line-of- sight to the network node 110. Alternatively, if the radio link or user requirements of wireless device(s) 121 may not be met without the assistance of the phase-shifting elements 131, i.e. the wireless device(s) 121 requires the gain offered by the phase- shifting elements 131 to be able to communicate reliably with the network node 110, a radio link or user characteristic weight equal to one (1) may be given to such a radio link characteristic or quality for that sub-band. This means that the radio link or user characteristic of this wireless device(s) 121 is relevant for the determination and configuration of the reflection state of the phase-shifting elements 131. This is because, in this case, the wireless device(s) 121 likely have poor cell coverage. It should also be noted that binary weighting as described above may also be useful in case where the entire bandwidth is allocated to a single wireless device 121. In that case, the sub-bands carrying control information to the single wireless device 121 may be assigned a weight equal to one (1), while the other sub-bands may be assigned a weight equal to zero (0). This may be performed in order to ensure that the single wireless device 121 is able to receive good quality control information transmissions. In some embodiments, if more than one wireless device(s) 121 is assigned to the same sub-band, e.g. more than one wireless device(s) 121 is scheduled in the same sub- band sequentially over time, then the resulting weight for that sub-band may be an average value of the weights for several or all the wireless device(s) 121 associated with that sub-band. In this case, the averaging of the weights for several or all the wireless devices 121 associated with a sub-band may, for example, be performed as a simple linear averaging, wherein the weights may be summed up and the sum is then divided by the total number of wireless devices 121 in that sub-band. Optionally, this may also be performed as a weighted linear averaging, wherein each weight may be multiplied by a unique coefficient, wherein the unique coefficient may be determined according to some parameter, for example, one of the radio link or user characteristics, such as, e.g. a priority of the wireless devices 121. The products of the multiplied weights and corresponding coefficients may then be summed up, and the result weight determined by dividing the sum by the total number of wireless devices 121 in that sub-band. In some embodiments, the weights for each sub-band may be updated as often as every scheduling instance or Transmission Time Interval, TTI. This is also close to the same time scale that the phase-shifting elements 131 conventionally change, correct or update their reflection states in order to provide a good propagation path between the network node 110 and the wireless device(s) 121. Therefore, the update rate of the weights for each sub-band need not be higher than the update rate of reflection states of the phase-shifting elements 131. In some embodiments, a wireless device(s) 121 with higher priority assigned by a scheduler, lower target Block Error Rates, BLERs, and / or higher throughput requirements may be given a larger weight for a sub-band than a wireless device(s) 121 with lower priority assigned by a scheduler, higher BLER requirement, higher target BLERs, and / or lower throughput requirements. This means that one or more wireless device(s) 121 may be prioritized and sub-bands being given larger priorities may be given larger weights. This means that one or more wireless device(s) 121 may be prioritized and the corresponding sub-bands given comparatively larger priorities may be assigned comparatively larger weights. In some embodiments, the network node 110 may determine the reflection state of the phase-shifting elements 131 based on the assigned weights and estimated Angle-of- Arrivals, AoAs, and Angle-of-Departures, AoDs, of the radio signals at the phase-shifting elements 131. This means, for example, that the network node 110 may estimate the AoA and AoD of the radio signals at the phase-shifting elements, e.g. at the reflective surface 130, and use this information to determine the reflection state of the phase-shifting elements 131 together with the assigned weights. The estimation of the AoA and AoD of the radio signals at the phase-shifting elements is known in the art and may, for example, be performed using channel estimation results. One example of how this may be performed is described in reference J. He, H. Wymeersch and M. Juntti, "Channel Estimation for RIS-Aided mmWave MIMO Systems via Atomic Norm Minimization," in IEEE Transactions on Wireless Communications, vol.20, no.9, pp.5786-5797, Sept. 2021, doi: 10.1109 / TWC.2021.3070064. In this case, according to some embodiments, the reflection state of the phase- shifting elements 131 may be determined by approximately maximizing a weighted beam gain caused by the phase-shifting elements 131 in the operating bandwidth of the radio signals using the assigned weights and the estimated Angle-of-Arrivals, AoAs, and Angle- of-Departures, AoDs, of the radio signals. This means that the network node 110 is able to determine suitable reflection states of the phase-shifting elements 131 that will cause a significantly improved weighted gain in a manner that is more practical and time-efficient, i.e. more computationally efficient, than to finding the exact reflection states of the phase- shifting elements 131 that will cause the optimal weighted beam gain. For example, using the weights for each sub-band as determined above, and estimated AoA and AoD of the radio signals at the phase-shifting elements 131, the network node 110 could configure the reflections states of the phase-shifting elements 131, i.e. reflective surface (RIS) phase shift values, by maximizing the weighted gain caused by the phase-shifting elements 131 according to Eq.5 : where ^^^^ is determined according to Eq.6: where ^^^^^^^^^^^^^^^^is the vector of unit-norm complex coefficients whose angles are the phase-shift values of the phase-shifting elements 131, ^^^^^^^^^^^^,^^^^and ^^^^^^^^^^^^^^^^,^^^^are array steering vectors corresponding to the frequency ^^^^^^^^and the given AoA and AoD, ^^^^^^^^is the corresponding real-valued weight for each sub-band ^^^^, and ^^^^^^^^is the number of sub-bands in the operating bandwidth. Here, it should be noted that the quantity ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^shows the weighted gain of the phase-shifting elements 131 for the operating bandwidth. However, it should also be noted that the original optimization problem is non- convex and hard to solve. According to some embodiments, in order to find an acceptablesolution, the constraint�[^^^^^^^^^^^^^^^^]^^^^� = 1, ^^^^ = 1, 2, … ,^^^^ may be relaxed to ^^^^^^^^^^^^^^^^^^^^ ^^^^^^^^^^^^^^^^ = ^^^^. Thissimplifies the problem to the standard Rayleigh quotient problem, wherein the optimal solution is found as the principal eigenvector of ^^^^ as seen below in Eq.7: Thus, in some embodiments, by applying an eigenvalue decomposition to ^^^^ the matrices ^^^^ and ^^^^ may be determined. Here, ^^^^ is unitary and ^^^^ is diagonal, where the term “diagonal” means that the diagonal elements are non-negative real numbers and sorted in decreasing order. Thus, the principal eigenvector ^^^^ may be found as the first column of ^^^^. However, according to some embodiments and as an alternative to applying eigenvalue decomposition to ^^^^, the well-known Power Iteration method may also here be used to determine the principal eigenvector ^^^^. In this case, the elements of the principal eigenvector ^^^^ may not be unit-normed themselves. However, in some embodiments, the phases of each element of the principal eigenvector ^^^^ to construct ^^^^^^^^^^^^^^^^instead, as shown below in Eq.8:^^^^^^^^^^^^^^^^ = ^^^^^^^^∠^^^^ (Eq. 8)In summary, according to some embodiments, the network node 110 may start by determining the matrix ^^^^ based on the array steering vectors corresponding to the frequency ^^^^^^^^, the estimated AoA and AoD of the radio signals at the phase-shifting elements 131, , and the weights ^^^^^^^^associated with eachsub-band ^^^^, namely{ . The network node 110 may then determine the eigenvector of the matrix ^^^^, namely ^^^^, and then configure the reflection states, i.e. phase-shift values, of the phase-shifting elements 131 according to ^^^^^^^^^^^^^^^^ = ^^^^^^^^∠^^^^. This means thatthe network node 110 may apply a closed-form formula for the reflection states, i.e. phase-shift values, of the phase-shifting elements 131, which makes it practical and time- efficient to implement, for example, using the well-known Power Iteration method. In some embodiments, the network node 110 may assign the weights to each of the different sub-bands based on their respective radio link and / or user characteristics of the radio signals in accordance with a higher-layer scheduling policy. This means that the most important criterion for the moment may, for example, be the output of an external entity, such as, e.g. the output of an Layer 3 (L3) or network layer scheduling policy. Here, for example, in case the most important criterion at the moment is to maximize capacity of the radio link, then radio link characteristics, such as, radio link gain or SNR, may be invoke a larger weight than other characteristics by the L3 scheduling policy. This is because these radio link characteristics are directly related to the radio link capacity and thus be the main parameters to use when optimizing the weights for the different sub- bands. If however, according to another example, the L3 scheduling policy decides that it is very urgent to empty a particular user's data buffer, then user characteristics, such as, the sub-band of that particular user, may invoke a larger weight than other characteristics by the L3 scheduling policy. In some embodiments, the network node 110 may transmit information indicating the reflection state of the phase-shifting elements 131 to a control unit 132 configured to control the phase-shifting elements 131. This means, for example, that the network node 110 may configure the reflection states of the phase-shifting elements 131 by informing the control unit 132 about the determined reflection states of the phase-shifting elements 131. Here, in some embodiments, the information indicates a reflection state of the phase- shifting elements 131 from a phase-shift codebook in the control unit 132. This means, for example, that the network node 110 may configure the reflection states of the phase- shifting elements 131 by determining a code word from a reflection state or phase shift codebook with an middle or center frequency determined as described in the above embodiments, and then transmit the code word, e.g. an index, to the control unit 132. For example, the network node 110 may select the codebook element from the reflection state or phase shift codebook, e.g. a codebook of reflective surface (RIS) phase-shift values, that yields the largest inner product with the setting of ^^^^^^^^^^^^^^^^and send the index of that codebook element to the control unit 132, e.g. a reflective surface (RIS) controller. This may be performed instead of, for example, informing the control unit 132 about the determined reflection states of the phase-shifting elements 131 by transmitting information explicitly indicating each of the reflections states or phase shifts per phase-shifting element 131. Further, as described above and according to some embodiments, the reflection state of the phase-shifting elements 131 comprise individual phase-shift values for each of the phase-shifting elements 131. Action 403 After configuring the reflection state of the phase-shifting elements 131 in Action 402, the network node 110 may transmit radio signals intended for the wireless devices 121 towards the phase-shifting elements 131. This means, for example, that the network node 110 may transmit the DL radio signals for the wireless device(s) 121 towards the phase-shifting elements 131 in order to take advantage of the gain offered by the phase- shifting elements 131 to be able to communicate reliably with the wireless device(s) 121. Reciprocally, the wireless device(s) 121 may similarly transmit UL radio signals for the network node 110 towards the phase-shifting elements 131 in order to also take advantage of the gain offered by the phase-shifting elements 131 and communicate reliably with the network node 110. Fig.5 shows a similar example of a typical scenario or use case for a reflective surface 130 comprising phase-shifting elements 131 as shown in Fig.1, except that the Angle-of-Arrivals, AoAs, and Angle-of-Departures, AoDs, of the radio signals has been defined, i.e. AoA = 10° and AoD = -60°, for the purpose of performing simulations, as described below, demonstrating the effect of some of the embodiments described herein. For the simulations, two (2) baseline techniques were used in order to be able to make comparisons. The first baseline technique, referred to as Baseline 1 or centered baseline, directly designs the phase shift values using the center frequency of the operating bandwidth without considering actual frequency channel used for the communication with the wireless device(s) 121, or any SNR distribution or requirement that may exist. Baseline 1 uses the formula in Eq.3 to evaluate and configure the reflection states of the phase-shifting elements 131, i.e. the phase-shift values of the reflective surface (RIS) 130. The second baseline technique, referred to as Baseline 2 or optimal baseline, finds the best carrier frequency at which the reflection states of the phase-shifting elements 131 is to be determined in order to maximize the weighted gain of the phase-shifting elements 131, i.e. the SNR gain of the reflective surface (RIS) 130. Baseline 2 applies a brute force search to find the frequency where the reflection states of the phase-shifting elements 131 should be designed. It should be noted that while Baseline 2 is aimed at maximizing the weighted SNR gain, the complexity of Baseline 2 is very high and which means it is only used here for illustrative purposes. In other words, Baseline 2 may be seen as optimal, but impractical. In the simulations, it is assumed that the operating bandwidth is 3 GHz with edge frequencies 25.5 GHz and 28.5 GHz, as shown in Fig.6. It is also assumed that a reflective surface (RIS) 130 with N = 1024 phase-shifting elements (32 x 32) is used that reflects the incoming signal from the angle AoA = 10° towards the angle AoD = -60°. In this example, all elevation angles are set to zero (0) for the sake of simplicity. Furthermore, for the simulations, the following weights of the sub-bands corresponding to the frequency ^^^^^^^^(in GHz) are assumed according to Eq.9: 5, 25.5 ≤ ^^^^^^^^ ≤ 26.5^^^^^^^^ =� 1, 26.5 < ^^^^^^^^ ≤ 27.5(Eq.9) 2, 27.5 < ^^^^^^^^ ≤ 28.5Here, a higher value of means that this sub-band is considered more important and thus prioritized. Fig.6 shows a diagram illustrating the reflective surface (RIS) gain of the phase- shifting elements 131 versus frequency resulting from simulations of the two (2) baseline techniques along with a simulation of a proposed technique according to some of the embodiments herein. In Fig.6, it may be seen that the proposed technique according to some of the embodiments herein has larger reflective surface (RIS) gains at frequencies / sub-bands with higher weights ^^^^^^^^. For instance, at 25.5 GHz which associated sub-band has a weight of 5, a 4.5 dB larger reflective surface (RIS) gain compared to Baseline 1 is obtained. In comparison to Baseline 2, the reflective surface (RIS) gains are nearly identical for the proposed technique according to some of the embodiments herein. By having the proposed technique according to some of the embodiments herein maintaining a near-optimal performance compared to the optimal, but impractical Baseline 2, the results clearly indicate that the proposed technique according to some of the embodiments herein effectively mitigates the squint effect at the more important sub-bands. To observe the effectiveness of the proposed technique according to some of the embodiments herein in a more general setting rather than the above example comprising the fixed weight setting according to Eq.9, a thousand (1000) Monte Carlo-simulations were performed. Here, at each trial, random weights for the sub-bands are selected uniformly from the interval [1, 10] for each sub-band, and the AoA and AoD are also randomly and uniformly selected from intervals [0°, 20°] and [-50°, -70°], respectively. The result of the Monte Carlo-simulations for two different cases, i.e. one with L=3 sub-bands and one with L=5 sub-bands, are shown and discussed below in Figs.7-10. Fig.7 shows a diagram illustrating a Cumulative Distribution Function, CDF, of the normalized weighted sum of the reflective surface (RIS) gain of the phase-shifting elements 131 resulting from the Monte Carlo-simulations with L=3 sub-bands. Here, the weighted sum of the reflective surface (RIS) gain of the phase-shifting elements 131 (^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^) is normalized by the total sum of weights as shown in Eq.10: nwsRISgain(Eq.10) where is the reflective surface (RIS) gain for wireless device(s) 121 for sub- band ^^^^, ^^^^^^^^is the weight assigned to sub-band ^^^^, and ^^^^ is the total number of sub-bands. According to Fig.7, it may be seen that the distribution of the weighted sum of the reflective surface (RIS) gain of the phase-shifting elements 131 for the proposed technique according to some of the embodiments herein is very close to that of the Baseline 2. On the other hand, there is a 0.6 dB median (50th percentile) gain enhancement, a 1.2 dB gain enhancement at the 10th percentile (10%), and even higher gains at lower percentiles which makes the proposed technique according to some of the embodiments herein a very suitable one to, for example, avoid potential outage situations. Fig.8 shows a diagram illustrating a CDF of the reflective surface (RIS) gain of the phase-shifting elements 131 at the sub-band with maximum weight (i.e. the most important or prioritized sub-band) resulting from the Monte Carlo-simulations with L=3 sub-bands. According to Fig.8, it may be seen that the reflective surface (RIS) gain of the phase-shifting elements 131 at the sub-band with the maximum weight is significantly enhanced for the proposed technique according to some of the embodiments herein as compared to Baseline 1. There is a 2.3 dB median gain enhancement and a 3.2 dB gain enhancement at 10thpercentile. Fig.9 shows a diagram illustrating a CDF of the normalized weighted sum of the reflective surface (RIS) gain of the phase-shifting elements 131 resulting from the Monte Carlo-simulations with L=5 sub-bands, while Fig.10 shows a diagram illustrating a CDF of the reflective surface (RIS) gain of the phase-shifting elements 131 at the sub-band with maximum weight resulting from the Monte Carlo-simulations with L=5 sub-bands. Similar results as seen in Figs.7-8 for L=3 sub-bands may be seen in Figs.9-10 for L=5 sub-bands. Here, it may be seen that the gain enhancement compared to Baseline 1 isslightly less for ^^^^ = 5 as compared to ^^^^ = 3. This is because when the number of sub-bands is higher and weights are independently chosen for different sub-bands, the probability of having a symmetric weighting around the middle or center frequency becomes higher. This will decrease the gap between the proposed technique according to some of the embodiments herein and Baseline 1. Nevertheless, even in this case, we observe a significant increase in the reflective surface (RIS) gain of the phase-shifting elements 131 for the proposed technique according to some of the embodiments herein over Baseline 1. To perform the method actions in a network node 110 for configuring the reflection state of phase-shifting elements 131 arranged to reflect radio signals between the network node 110 and wireless devices 121 served by the network node 110 in a wireless communications network 100, the network node 110 may comprise the following arrangement depicted in Fig.11. Fig.11 shows a schematic block diagram of embodiments of the network node 110. The network node 110 may comprise processing circuitry or processor 1110 and a memory 1120. The processing circuitry 1110 may also comprise a receiving module 1111 and a transmitting module 1112. The receiving module 1111 and the transmitting module 1112 may also be configured to communicate and perform transmissions over the wireless communications network 100. The receiving module 1111 and the transmitting module 1112 comprise Radio Frequency, RF, processing circuitry capable of transmitting a radio signal via a radio interface (not shown) within the wireless communications network 100. The receiving module 1111 and the transmitting module 1112 may also form part of a single transceiver. It should also be noted that some or all of the functionality described in the embodiments above as being performed by the network node 110 may be provided by the processing circuitry 1110 executing instructions stored on a computer-readable medium, such as, e.g., the memory 1120 shown in Fig.11. Alternative embodiments of the network node 110 may comprise additional components, such as, for example, an obtaining module 1113, and a configuring module 1114, each responsible for providing its respective functionality necessary to support the embodiments described herein. The network node 110 or processing circuitry 1110 is configured to, or may comprise the obtaining module 1113 configured to, obtain radio link and / or user characteristics for different sub-bands of the operating bandwidth of the radio signals. Also, the network node 110 or processing circuitry 1110 is configured to, or may comprise the configuring module 1114 configured to, configure the reflection state of the phase- shifting elements 131 by assigning different weights to the different sub-bands, wherein the weights are determined based on their respective sub-band’s radio link and / or user characteristics. In some embodiments, the network node 110 or processing circuitry 1110 may be configured to, or may comprise the configuring module 1114 configured to, determine the reflection state of the phase-shifting elements 131 based on the assigned weights and estimated Angle-of-Arrivals, AoAs, and Angle-of-Departures, AoDs, of the radio signals at the phase-shifting elements 131. In this case, according to some embodiments, the reflection state of the phase-shifting elements 131 is determined by approximately maximizing a weighted beam gain caused by the phase-shifting elements 131 in the operating bandwidth of the radio signals using the assigned weights and the estimated Angle-of-Arrivals, AoAs, and Angle-of-Departures, AoDs, of the radio signals. In some embodiments, the weights are assigned to each of the different sub-bands based on their respective radio link and / or user characteristics of the radio signals in accordance with a higher-layer scheduling policy. According to some embodiments, the radio link characteristics for the different sub-bands of the operating bandwidth of the radio signals may comprise one or more of: a bandwidth assigned to the sub-band; a primary cell, pCell, bandwidth assigned to the sub- band; an AoA of radio signals to the served wireless devices 121 in the sub-band; an AoD of radio signals to the served wireless devices 121 in the sub-band; a type of a radio link in the sub-band; a quality or gain of a radio link to a served wireless device(s) 121 in the sub-band; a path-loss of a radio link to a served wireless device(s) 121 in the sub-band; and a Signal-to-Noise Ratio, SNR, of a radio link to a served wireless device(s) 121 in the sub-band. Further, in some embodiments, the user characteristics for the different sub- bands of the operating bandwidth of the radio signals may comprise one or more of: the number of served wireless devices 121 in the sub-band; a Quality-of-Service, QoS, requirement of one or more served wireless devices 121 in the sub-band; a priority of one or more served wireless devices 121 in the sub-band; and a priority of a control or data channel to / from one or more served wireless device(s) 121 in the sub-band. In some embodiments, the network node 110 or processing circuitry 1110 may be configured to, or may comprise the transmitting module 1112 configured to, transmit information indicating the reflection state of the phase-shifting elements 131 to a control unit 132 configured to control the phase-shifting elements 131. Here, in some embodiments, the information indicates a reflection state of the phase-shifting elements 131 from a phase-shift codebook in the control unit 132. Furthermore, in some embodiments, the reflection state of the phase-shifting elements 131 comprise individual phase-shift values for each of the phase-shifting elements 131. In some embodiments, the network node 110 or processing circuitry 1110 may be configured to, or may comprise the transmitting module 1112 configured to, transmit radio signals intended for the wireless devices 121 towards the phase-shifting elements. Furthermore, the embodiments for adapting processing capacity in processing units 102-105 arranged to serve wireless devices 111, 112 in a wireless communications network 100 described above may be implemented through one or more processors, such as the processing circuitry 1510 in the network node 110 depicted in Fig.15, together with computer program code for performing the functions and actions of the embodiments herein. The program code mentioned above may also be provided as a computer program product, for instance in the form of a data carrier carrying computer program code or code means for performing the embodiments herein when being loaded into the processing circuitry 1510 in the network node 110. The computer program code may e.g. be provided as pure program code in the network node 110 or on a server and downloaded to the network node 110. Thus, it should be noted that the modules of the network node 110 may in some embodiments be implemented as computer programs stored in memory, e.g. in the memory modules 1520 in Fig.15, for execution by processors or processing modules, e.g. the processing circuitry 1510 of Fig.15. Those skilled in the art will also appreciate that the processing circuitry 1510 and the memory 1520 described above may refer to a combination of analog and digital circuits, and / or one or more processors configured with software and / or firmware, e.g. stored in a memory, that when executed by the one or more processors such as the processing circuitry 1520 perform as described above. One or more of these processors, as well as the other digital hardware, may be included in a single application-specific integrated circuit (ASIC), or several processors and various digital hardware may be distributed among several separate components, whether individually packaged or assembled into a system-on-a-chip (SoC). The description of the example embodiments provided herein have been presented for purposes of illustration. The description is not intended to be exhaustive or to limit example embodiments to the precise form disclosed, and modifications and variations are possible in light of the above teachings or may be acquired from practice of various alternatives to the provided embodiments. The examples discussed herein were chosen and described in order to explain the principles and the nature of various example embodiments and its practical application to enable one skilled in the art to utilize the example embodiments in various manners and with various modifications as are suited to the particular use contemplated. The features of the embodiments described herein may be combined in all possible combinations of methods, apparatus, modules, systems, and computer program products. It should be appreciated that the example embodiments presented herein may be practiced in any combination with each other. It should be noted that the word “comprising” does not necessarily exclude the presence of other elements or steps than those listed and the words “a” or “an” preceding an element do not exclude the presence of a plurality of such elements. It should further be noted that any reference signs do not limit the scope of the claims, that the example embodiments may be implemented at least in part by means of both hardware and software, and that several “means”, “units” or “devices” may be represented by the same item of hardware. It should also be noted that the various example embodiments described herein are described in the general context of method steps or processes, which may be implemented in one aspect by a computer program product, embodied in a computer- readable medium, including computer-executable instructions, such as program code, executed by computers in networked environments. A computer-readable medium may include removable and non-removable storage devices including, but not limited to, Read Only Memory (ROM), Random Access Memory (RAM), compact discs (CDs), digital versatile discs (DVD), etc. Generally, program modules may include routines, programs, objects, components, data structures, etc. that perform particular tasks or implement particular abstract data types. Computer-executable instructions, associated data structures, and program modules represent examples of program code for executing steps of the methods disclosed herein. The particular sequence of such executable instructions or associated data structures represents examples of corresponding acts for implementing the functions described in such steps or processes. The embodiments herein are not limited to the above described preferred embodiments. Various alternatives, modifications and equivalents may be used. Therefore, the above embodiments should not be construed as limiting.

[0002] ABBREVIATIONS

Claims

CLAIMS 1. A method performed by a network node (110) for configuring the reflection state of phase-shifting elements (131) arranged to reflect radio signals between the network node (110) and wireless devices (121) served by the network node (110) in a wireless communications network (100), the method comprising obtaining (401) radio link and / or user characteristics for different sub-bands of the operating bandwidth of the radio signals; and configuring (402) the reflection state of the phase-shifting elements (131) by assigning different weights to the different sub-bands, wherein the weights are determined based on their respective sub-band’s radio link and / or user characteristics.

2. The method according to claim 1, further comprising determining the reflection state of the phase-shifting elements (131) based on the assigned weights and estimated Angle-of-Arrivals, AoAs, and Angle-of-Departures, AoDs, of the radio signals at the phase-shifting elements (131).

3. The method according to claim 2, wherein the reflection state of the phase-shifting elements (131) is determined by approximately maximizing a weighted beam gain caused by the phase-shifting elements (131) in the operating bandwidth of the radio signals using the assigned weights and the estimated Angle-of-Arrivals, AoAs, and Angle-of-Departures, AoDs, of the radio signals.

4. The method according to any of claims 1-3, wherein the weights are assigned to each of the different sub-bands based on their respective radio link and / or user characteristics of the radio signals in accordance with a higher-layer scheduling policy.

5. The method according to any of claims 1-4, wherein the radio link characteristics for the different sub-bands of the operating bandwidth of the radio signals comprise one or more of: - a bandwidth assigned to the sub-band; - a primary cell, pCell, bandwidth assigned to the sub-band; - an AoA of radio signals to the served wireless devices (121) in the sub- band;- an AoD of radio signals to the served wireless devices (121) in the sub- band; - a type of a radio link in the sub-band; - a quality or gain of a radio link to a served wireless device (121) in the sub-band; - a path-loss of a radio link to a served wireless device (121) in the sub- band; and - a Signal-to-Noise Ratio, SNR, of a radio link to a served wireless device (121) in the sub-band.

6. The method according to any of claims 1-5, wherein the user characteristics for the different sub-bands of the operating bandwidth of the radio signals comprise one or more of: - the number of served wireless devices (121) in the sub-band; - a Quality-of-Service, QoS, requirement of one or more served wireless devices (121) in the sub-band; - a priority of one or more served wireless devices (121) in the sub-band; and - a priority of a control or data channel to / from one or more served wireless device (121) in the sub-band.

7. The method according to any of claims 1-6, further comprising transmitting information indicating the reflection state of the phase-shifting elements (131) to a controller (132) configured to control the phase-shifting elements (131).

8. The method according to claim 7, wherein the information indicates a reflection state of the phase-shifting elements (131) from a phase-shift codebook in the controller (132).

9. The method according to any of claims 1-8, wherein the reflection state of the phase-shifting elements (131) comprise individual phase-shift values for each of the phase-shifting elements (131).

10. The method according to any of claims 1-9, further comprisingtransmitting (403) radio signals intended for the wireless devices (121) towards the phase-shifting elements (131).

11. The method according to any of claims 1-10, wherein the phase-shifting elements (131) form part of a reflective surface or Reconfigurable Intelligent Surface, RIS, arrangement (130).

12. A network node (110) for configuring the reflection state of phase-shifting elements (131) arranged to reflect radio signals between the network node (110) and wireless devices (121) served by the network node (110) in a wireless communications network (100), the network node (110) being configured to obtain radio link and / or user characteristics for different sub-bands of the operating bandwidth of the radio signals, and configure the reflection state of the phase-shifting elements (131) by assigning different weights to the different sub- bands, wherein the weights are determined based on their respective sub-band’s radio link and / or user characteristics.

13. The network node (110) according to claim 12, further configured to determine the reflection state of the phase-shifting elements (131) based on the assigned weights and estimated Angle-of-Arrivals, AoAs, and Angle-of-Departures, AoDs, of the radio signals at the phase-shifting elements (131).

14. The network node (110) according to claim 13, wherein the reflection state of the phase-shifting elements (131) is determined by approximately maximizing a weighted beam gain caused by the phase-shifting elements (131) in the operating bandwidth of the radio signals using the assigned weights and the estimated Angle- of-Arrivals, AoAs, and Angle-of-Departures, AoDs, of the radio signals.

15. The network node (110) according to any of claims 12-14, wherein the weights are assigned to each of the different sub-bands based on their respective radio link and / or user characteristics of the radio signals in accordance with a higher-layer scheduling policy.

16. The network node (110) according to any of claims 12-15, wherein the radio link characteristics for the different sub-bands of the operating bandwidth of the radio signals comprise one or more of: - a bandwidth assigned to the sub-band; - a primary cell, pCell, bandwidth assigned to the sub-band; - an AoA of radio signals to the served wireless devices (121) in the sub- band; - an AoD of radio signals to the served wireless devices (121) in the sub- band; - a type of a radio link in the sub-band; - a quality or gain of a radio link to a served wireless device (121) in the sub-band; - a path-loss of a radio link to a served wireless device (121) in the sub- band; and - a Signal-to-Noise Ratio, SNR, of a radio link to a served wireless device (121) in the sub-band.

17. The network node (110) according to any of claims 12-16, wherein the user characteristics for the different sub-bands of the operating bandwidth of the radio signals comprise one or more of: - the number of served wireless devices (121) in the sub-band; - a Quality-of-Service, QoS, requirement of one or more served wireless devices (121) in the sub-band; - a priority of one or more served wireless devices (121) in the sub-band; and - a priority of a control or data channel to / from one or more served wireless device (121) in the sub-band.

18. The network node (110) according to any of claims 12-17, further configured to transmit information indicating the reflection state of the phase-shifting elements (131) to a control unit (132) configured to control the phase-shifting elements (131).

19. The network node (110) according to claim 18, wherein the information indicates a reflection state of the phase-shifting elements (131) from a phase-shift codebook in the control unit (132).

20. The network node (110) according to any of claims 12-19, wherein the reflection state of the phase-shifting elements (131) comprise individual phase-shift values for each of the phase-shifting elements (131).

21. The network node (110) according to any of claims 12-20, further configured to transmit radio signals intended for the wireless devices (121) towards the phase- shifting elements.

22. The network node (110) according to any of claims 12-21, comprising at least one processor (1110) and a memory (1120), wherein the memory (1120) is containing instructions executable by the at least one processor (1101).

23. A computer program, comprising instructions which, when executed on at least one processor (1110), cause the at least one processor (1110) to carry out the method according to any of claims 1-11.

24. A carrier containing the computer program according to claim 23, wherein the carrier is one of an electronic signal, optical signal, radio signal, or computer- readable storage medium.

Images